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目的 研究缓症链球菌外毒素蛋白的分子量、等电点、氨基酸组成及N 末端序列。方法 将纯化的毒素蛋白用SDS PAGE电泳 ,据低分子量标准蛋白质算出其相对分子质量 ;以微型聚丙烯酰胺等电聚焦 (miniIEF)法进行此毒素蛋白的等点电测定 ;采用电印迹将SDS PAGE电泳胶上的毒素蛋白转移到PVDF膜上 ,用Beckman 34 4HPLC仪测定外毒素蛋白的氨基酸组成 ;用自动化蛋白质序列仪测定缓症链球菌外毒素N 末端氨基酸序列。结果 缓症链球菌外毒素蛋白的相对分子质量为 34 0 0 0 ;测定毒素蛋白的等点电为 6 .2 ,是一种偏酸性蛋白 ;外毒素蛋白由 1 7种氨基酸组成 ,其中谷氨酸、甘氨酸、丙氨酸、门冬氨酸、赖氨酸、缬氨酸等氨基酸含量较高 ;缓症链球菌外毒素蛋白N 末端氨基酸序列为 :VSNLSRGMGA ,本毒素N 末端氨基酸序列与β溶血链球菌外毒素蛋白 (SPEA、SPEB、SEPC)N 末端氨基酸序列不同。结论 此外毒素蛋白的分子量、等电点、氨基酸组成和末端氨基酸序列均与其他 β溶血性链球菌外毒素不同 ,可能是一种新的链球菌致热性外毒素
Objective To study the molecular weight, isoelectric point, amino acid composition and N-terminal sequence of Streptococcus mutans exotoxin protein. Methods The purified toxin protein was electrophoresed on SDS PAGE and its relative molecular weight was calculated from low molecular weight standard protein. The isoelectric point of this toxin protein was determined by miniIEF method. SDS PAGE The toxin protein on the gel was transferred to a PVDF membrane and the amino acid composition of the exotoxin protein was determined on a Beckman 34 4HPLC instrument. The N-terminal amino acid sequence of S. exuviate endotoxin was determined using an automated protein sequencer. Results The relative molecular mass of Streptococcus mitis exo toxin protein was 3400. The isoelectric point of the toxin protein was 6.2, which was a kind of acidic protein. The exotoxin protein consisted of 17 kinds of amino acids, Glycine, Alanine, Aspartic acid, Lysine and Valine. The N-terminal amino acid sequence of Streptococcus sovulins exotoxin protein is: VSNLSRGMGA. The N-terminal amino acid sequence of the toxin and β-hemolysis Streptococcus exotoxin protein (SPEA, SPEB, SEPC) N-terminal amino acid sequence is different. Conclusion In addition, the molecular weight, isoelectric point, amino acid composition and terminal amino acid sequence of toxin protein are different from those of other β-hemolytic streptococcus exotoxins, and may be a new streptococcus thermotoxin exotoxin